Mixed voice and spread spectrum data signaling with enhanced concealment of data

ABSTRACT

Systems, methods, and devices for mixed voice and spread spectrum data signaling with enhanced concealment of data are disclosed. Audible artifacts may be reduced or suppressed in order to improve the audible quality of the sound. The distortion to the audio may be kept just below perceptibility, yet the data contained within the modulated signal is recoverable on the receiving side. The recovery of the data is robust to the impairments imposed by the communication channel. The disclosed systems, methods, and devices may be implemented in audio conferencing or video conferencing. Various embodiments of the present disclosure provide a data and voice mixer, which includes an improved spread spectrum data hiding transmitter. The transmitter may comprise a spreading encoder, a Phase Shift Keying (PSK) modulator, and a notch filter. A pseudo random switching pattern may be applied to a plurality of chip sequence generators in order to reduce or suppress an undesirable audible artifact. The transmitter may further comprise a phase randomizer operable to rotate the phase of the output of the spreading encoder by a pseudo random increment of approximately 45 degrees.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending Ser. No.11/148,087 filed on Jun. 8, 2005 entitled “Voice Interference Correctionfor Mixed Voice and Spread Spectrum Data Signaling.” The benefit ofpriority of 35 U.S.C. §120 is hereby claimed. The contents of thereferenced application are hereby incorporated by reference.

This application is related to Ser. No. 11/536,546 filed on even dateherewith entitled “Mixed Voice and Spread Spectrum Data Signaling withMultiplexing Multiple Users with CDMA.” The contents of the referencedapplication are hereby incorporated by reference.

This application is also related to the following co-pendingapplications, all of which are commonly assigned and were filed on Mar.15, 2005: Ser. No. 11/081,081 entitled “Conference Endpoint ControllingFunctions of a Remote Device”; Ser. No. 11/080,369, entitled “ConferenceEndpoint Controlling Audio Volume of a Remote Device”; Ser. No.11/080,989, entitled “Conference Endpoint Instructing Conference Bridgeto Dial Phone Number”; Ser. No. 11/080,993, entitled “ConferenceEndpoint Instructing Conference Bridge to Mute Participants”; Ser. No.11/080,985, entitled “Conference Endpoint Instructing a Remote Device toEstablish a New Connection”; Ser. No. 11/081,019, entitled “ConferenceEndpoint Requesting and Receiving Billing Information from a ConferenceBridge”; Ser. No. 11/080,997, entitled “Speakerphone Transmitting URLInformation to a Remote Device”; Ser. No. 11/080,988, entitled“Speakerphone Using a Secure Audio Connection to Initiate a SecondSecure Connection”; Ser. No. 11/080,984, entitled “Speakerphone andConference Bridge which Request and Perform Polling Operations”; Ser.No. 11/081,016, entitled “Speakerphone Transmitting Password Informationto a Remote Device”; Ser. No. 11/080,995, entitled “Speakerphone andConference Bridge which Receive and Provide Participant MonitoringInformation”; Ser. No. 11/080,999, entitled “Speakerphone Establishingand Using a Second Connection of Graphics Information”; Ser. No.11/080,994, entitled “Conference Bridge Which Decodes and Responds toControl Information Embedded in Audio Information”; Ser. No. 11/080,996,entitled “Conference Bridge Which Detects Control Information Embeddedin Audio Information to Prioritize Operations”; Ser. No. 11/080,978,entitled “Conference Bridge Which Transfers Control Information Embeddedin Audio Information Between Endpoints”; and Ser. No. 11/080,977,entitled “Speakerphone Transmitting Control Information Embedded inAudio Information Through a Conference Bridge.” The contents of theaforementioned applications are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Without limiting the scope of the invention, the present inventionrelates generally to embedding digital data in an audio signal, and moreparticularly, to systems, methods, and devices for spread spectrum datahiding with enhanced concealment of data.

2. Description of the Related Art

During a phone call, a participant may desire to not only transmit voicebut to also supplement the voice with data content. An audio systemwhich can transmit additional data has many different uses. For example,such additional data may be related to an ongoing teleconference(referred to herein as conference). For example, the data may be relatedto an ongoing audio conference or video conference.

The data is digital, while the voice is analog. There are a number ofways to combine digital data and voice signals together. For example,one way is to use digital telephone channels such as an internet link orISDN-based channels. The digital data can be multiplexed with digitizedvoice. This method is limited, however, to channels that are digitalend-to-end.

Another way to combine digital data and voice signals is to use a modemtechnology such as V.34 or V.92. This will also provide a digitalchannel for multiplexing digital data with digitized voice. The basechannel can be analog. A drawback exists, however, in that the modemloses periods of audio, for example, while the modem trains and duringbit errors and retrains. Moreover, the modem solution only workspoint-to-point and only works with compatible systems.

Yet another way is to use spread spectrum modulation of the data overthe full phone line bandwidth. Energy at a frequency is spread over awide range of frequencies for transmission, and the spread spectrumsignals are collected onto their original frequency at the receiver.Spread spectrum techniques use noise-like carrier waves which aregenerally regarded as difficult to detect and demodulate. It is achallenge to balance restraining the audibility of the modulated dataand assuring the reliability of its decoding.

BRIEF SUMMARY OF THE INVENTION

Various embodiments of the present disclosure provide systems, methods,and devices for adding modulated data to an analog audio signal, withenhanced concealment of the data. Audible artifacts may be reduced orsuppressed in order to improve the audible quality of the sound. Thedistortion to the audio may be kept just below perceptibility, yet thedata contained within the modulated signal is recoverable on thereceiving side. The recovery of the data is robust to the impairmentsimposed by the communication channel.

In accordance with various embodiments of the present disclosure, amethod of preparing an analog audio signal and a digital bit stream fortransmission via a communication channel is provided. The method mayinclude generating a chip sequence; combining the digital bit stream andthe chip sequence, to form a spread spectrum sequence; modulating thespread spectrum sequence onto the audio signal, to form a modulatedsignal; and suppressing one or more noise-like artifacts of themodulated signal. The act of suppressing may include comprise applying anotch filter in a narrow band in order to attenuate the modulated signalnear a carrier frequency. The act of suppressing may include rotating aphase of the spread spectrum sequence by a pseudo-random increment everychip. The method may further include demodulating a received signal, toproduce a demodulated signal; de-randomizing the demodulated signal, bymultiplying the demodulated signal by a complex conjugate of a pseudorandom phase pattern, to produce a phase envelope sequence; andmultiplying the phase envelope sequence by the chip sequence, to producethe recovered bit stream.

Various embodiments of the present disclosure also provide an audioconferencing endpoint, including at least one microphone and at leastone speaker. The endpoint may further include an audio and data mixer,comprising a first chip sequence generator operable to generate a firstchip sequence; a spreading encoder operable to combine a digital bitstream and the first chip sequence, to form a spread spectrum sequence;a phase randomizer operable to rotate a phase of the spread spectrumsequence by a pseudo-random increment every chip; and a modulatoroperable to modulate the rotated spread spectrum sequence onto an analogaudio signal received from the at least one microphone, to form amodulated signal. The endpoint may further include an audio and dataseparator, comprising a demodulator operable to demodulate a receivedsignal, to produce a demodulated signal; a phase de-randomizer operableto de-randomize the demodulated signal, by multiplying the demodulatedsignal by a complex conjugate of a pseudo random phase pattern, toproduce a phase envelope sequence; a second chip sequence generator,operable to generate a second chip sequence; and a spreading decoderoperable to multiply the phase envelope sequence by the second chipsequence, to reconstruct a received bit stream.

Various embodiments of the present disclosure further provide an audioconferencing system wherein data and audio may be exchanged among aplurality of endpoints. At least one of the endpoints may include aspread spectrum data hiding transmitter capable of combining data andaudio, with suppression of noise-like artifacts. Another of theendpoints may include a data and audio separator. In accordance withsome embodiments, some of the endpoints may be incapable of separatingdata from a received signal; however, when the received signal isreproduced as sound, the data may have been hidden by the transmitter insuch a way as to be perceived as sounding like white noise or no noiseat all.

In accordance with various embodiments of the present disclosure, amachine-readable medium may have embodied thereon a program which isexecutable by a machine to perform a method described herein.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A better understanding of the invention can be had when the followingdetailed description of the preferred embodiments is considered inconjunction with the following drawings, in which:

FIG. 1 depicts a block diagram of an exemplary data and voice mixer inaccordance with various embodiments of the present disclosure;

FIG. 2A depicts a block diagram of an exemplary SSDH transmitter inaccordance with one embodiment of the present disclosure;

FIG. 2B depicts a block diagram of an exemplary SSDH transmitter inaccordance with another embodiment of the present disclosure;

FIG. 3 depicts a block diagram of an exemplary CDMA chip sequencegenerator in accordance with various embodiments of the presentdisclosure;

FIG. 4 depicts a block diagram of an exemplary spreading encoder inaccordance with various embodiments of the present disclosure;

FIG. 5 depicts a block diagram of an exemplary spreading encoder andspreading decoder in accordance with various embodiments of the presentdisclosure;

FIG. 6 depicts a block diagram of an exemplary PSK modulator inaccordance with various embodiments of the present disclosure;

FIG. 7 depicts a block diagram of an exemplary PSK demodulator inaccordance with various embodiments of the present disclosure;

FIG. 8 depicts a block diagram of an exemplary low buzz CDMA chipsequence generator in accordance with various embodiments of the presentdisclosure;

FIG. 9 depicts a block diagram of an exemplary phase randomizer inaccordance with various embodiments of the present disclosure;

FIG. 10 depicts a block diagram of an exemplary phase de-randomizer inaccordance with various embodiments of the present disclosure;

FIG. 11A depicts a block diagram of an exemplary modulator in accordancewith one embodiment of the present disclosure;

FIG. 11B depicts a block diagram of an exemplary modulator in accordancewith another embodiment of the present disclosure;

FIG. 12 depicts a block diagram of an exemplary demodulator inaccordance with various embodiments of the present disclosure;

FIG. 13 depicts a block diagram of an exemplary data and voice mixer inaccordance with various embodiments of the present disclosure;

FIG. 14 depicts a block diagram of an exemplary Forward Error Correctionencoder in accordance with various embodiments of the presentdisclosure;

FIG. 15 depicts a block diagram of an exemplary Forward Error Correctiondecoder in accordance with various embodiments of the presentdisclosure;

FIG. 16 depicts a block diagram of an exemplary sync pattern inserter inaccordance with various embodiments of the present disclosure;

FIG. 17 depicts a block diagram of an exemplary masking shaper inaccordance with various embodiments of the present disclosure;

FIG. 18 depicts a block diagram of an exemplary spectral shape extractorin accordance with various embodiments of the present disclosure;

FIG. 19 depicts a block diagram of an exemplary masking shaping filterin accordance with various embodiments of the present disclosure;

FIG. 20 depicts a block diagram of an exemplary whitening equalizer inaccordance with various embodiments of the present disclosure;

FIG. 21 depicts a block diagram of an exemplary data and voice separatorin accordance with various embodiments of the present disclosure; and

FIG. 22 depicts a block diagram of an exemplary conferencing system inaccordance with various embodiments of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention provide systems, methods,and devices for data hiding with improved transparency by reducinghumanly audible artifacts. Data hiding allows digital information to beconcealed within a cover media such as, for example, audio, video, orimages. The measure of concealment, commonly termed transparency, isenhanced by exploiting the perceptual limits of human hearing or vision.In the case of data hiding within audio, transparency may be aided byfiltering the modulated data signal so as to achieve a target temporaland spectral shape.

It is found that one way to lower perceptibility of the noise associatedwith the additional data in an audio signal is to use spread spectrumtechniques. The spread spectrum method is generally regarded as robustagainst jamming and interference. It can be hidden and masked due to thelow amplitude at any given frequency, and it is robust such that even ifmany channels are impaired, the overall signal can still go through. Thespread spectrum can naturally support multi-user implementation; forexample, it is used in the CDMA (Code Division Multiple Access) cellulartelephone system.

In accordance with various embodiments of the present disclosure, spreadspectrum data hiding (SSDH) is provided wherein modulated data is addedto an analog voice signal with the modulated data generated by a spreadspectrum modem. A block diagram of an exemplary data and voice mixer 100is depicted in FIG. 1. A voice signal 110 to be transmitted is denotedby voice(t), wherein t represents continuous time. A delay unit 120 maybe included to align the voice signal 110 for proper cancellation. Thedelay may be a function of implementation.

The binary sequence 130 to be transmitted is denoted by data(m), whereinm represents raw data bit time. The binary sequence 130 is fed into anSSDH transmitter 140. Various embodiments of the SSDH transmitter 140are described below in more detail. The output of the SSDH transmitter140 is a modulated distortion signal 150, μ(t). The distortion to theaudio may be kept just below humanly perceptible levels. The datacontained within μ(t) is recoverable on the receiving side by a voiceand data separator. The recovery of the data may be regarded as robustto the interference of the voice(t) signal and the impairments imposedby the telephone channel.

The modulated distortion signal 150 may be added with the output of thedelay unit 120 to produce a transmitter signal 160 denoted as x(t). Thetransmitter signal 160 may be used as an input to, for example, atelephone channel or other communication channel.

Reference is now made to FIG. 2A which depicts a block diagram of anexemplary SSDH transmitter in accordance with one embodiment of thepresent disclosure. The SSDH transmitter may comprise a chip sequencegenerator 220 which generates a periodic chip pattern c(k). A userselect 210 may provide one or more initial values for the linearfeedback shift register producing the spreading chip sequence, q(k). TheSSDH transmitter may further comprise a spreading encoder 230. Thespreading encoder 230 multiplies a bit sequence b(n) and the chippattern c(k) to produce a phase envelope sequence, σ(k). The SSDHtransmitter may further comprise a PSK (Phase Shift Keying) modulator240. PSK describes a modulation technique that conveys data by alteringthe phase of the carrier wave. The SSDH transmitter may further comprisean AC notch filter 250 for attenuating a desired carrier frequency, asdescribed in more detail below. In accordance with another exemplaryembodiment as depicted in FIG. 2B, the SSDH transmitter may comprise aDC notch filter 260, instead of the AC notch filter 250, as described inmore detail below.

In accordance with one embodiment of the present disclosure, it may bedesirable to allow for users from many locations to be connectedtogether in a conference call and share data. A problem of sharing asingle audio channel for multiple data streams arises. In the simplestcase of a point-to-point call, there are only two users. The two usersare able to share the single channel by use of random back offs and/orline echo cancellation.

For more than two users, the spread spectrum encoder may include CDMA.This is done by using different spreading codes for different userswhich are nearly orthogonal to each other. That is, the crosscorrelation may be minimized as follows:

$\begin{matrix}{{{{cost}\mspace{14mu}{to}\mspace{14mu}\min} = {\sum\limits_{{k = 1},2,{\ldots\mspace{11mu} L}}{{C\left( {{userA},k} \right)}{C\left( {{userB},{k + m}} \right)}}}}\mspace{11mu}{{{{for}\mspace{14mu}{all}\mspace{14mu} m\mspace{14mu}{and}\mspace{14mu}{all}\mspace{14mu}{userA}} \neq {userB}},}} & {{Eq}.\mspace{14mu} 1}\end{matrix}$

wherein k represents chip time, i.e., discrete time, and L representsthe period or length of the spreading chip sequence.

A solution for the above criteria may be provided by a pseudonoise (PN)sequence which may be provided by the Gold codes. They can be generatedwith two linear feedback shift register produced bit sequences which areXORed together. FIG. 3 depicts a block diagram of an exemplary CDMA chipsequence generator 300. In accordance with various embodiments of thepresent disclosure, the chip sequence generator 220 of FIG. 2A or 2B maybe embodied as the CDMA chip sequence generator 300 of FIG. 3. In thisexample, L is 31 chips per symbol. Different users are obtained byselecting different initializations for the registers. All combinationsof initializations may be tried to find the best combinations tominimize the cross correlation.

Referring again to FIGS. 2A and 2B, the spreading encoder 230 may beembodied as shown in FIG. 4, which depicts a block diagram of anexemplary spreading encoder 400 in accordance with various embodimentsof the present disclosure. In one embodiment, the spreading encoder 400may utilize direct sequence spread spectrum (DSSS) techniques. Thespreading encoder 400 multiplies a bit sequence 410, denoted as b(n),and a chip pattern 420, denoted as c(k), to produce a phase envelopesequence 430, denoted as σ(k). The bit sequence 410 to the spreadingencoder 410 represents a symbol sign on the transmitter of +1 or −1.

In accordance with a DSSS technique, a spreading chip sequence q(k) maybe defined as follows:q(k) are elements of {−1, 1} only defined for indexes k over {1, 2, 3, .. . , L}.  Eq. 2

The periodic chip pattern c(k) may be defined as follows:c(k)=q((k−1)mod L)+1),for all integers k.  Eq. 3That is,c(k+nL)=q(k),  Eq. 4

where n is over all integers and k is over {1, 2, 3, . . . L}.

The chip sequence pattern may be designed with criteria as follows:

$\begin{matrix}{{{\sum\limits_{{k = 1},2,{\ldots\mspace{11mu} L}}{{C(k)}{C(k)}}} = L},} & {{Eq}.\mspace{14mu} 5}\end{matrix}$

and the offset correlation may be minimized as follows:

$\begin{matrix}{{{cost}\mspace{14mu}{to}\mspace{14mu}\min} = {{\sum\limits_{{k = 1},2,{\ldots\mspace{11mu} L}}{{C(k)}{C\left( {k + m} \right)}\mspace{14mu}{for}\mspace{14mu} m}} \neq 0}} & {{Eq}.\mspace{14mu} 6}\end{matrix}$

The index n represents symbol time running at a period of T_(sym). Theperiod T_(sym) may be set such thatT _(sym) =LT _(c)  Eq. 7

The synchronous chip time k from the bit time n may be computed with thefollowing relationship:k=nL  Eq. 8

The inverse is computed as follows:n=└k/L┘,  Eq. 9

wherein └•┘ is the floor operator. We can now define how we generateσ(k) from the symbol sequence as follows:σ(k)=c(k)b(└k/L┘)  Eq. 10

Reference is now made to FIG. 5 which depicts a block diagram of anexemplary spreading decoder 500 in communication with the spreadingencoder 400 of FIG. 4 in accordance with various embodiments of thepresent disclosure. A communication channel 510 such as, for example, atelephone channel or a radio channel, provides a link between theencoding side and the decoding side. At the receiver side afterdemodulation of a clean synchronized signal, we find as follows:ρ(k)=σ(k)=c(k)b(└k/L┘),  Eq. 11

wherein ρ(k) represents the received phase envelope at output of a PSKDemodulator, as explained in more detail below.

We now multiply by the chip sequence pattern one more time, as follows:c(k)ρ(k)=c ²(k)b(└k/L┘)  Eq. 12

Note that since c(k) is from the set {−1, 1}, it follows that c²(k)=1such thatc(k)ρ(k)=b(└k/L┘)  Eq. 13

A true channel will have noise to average out. This can be achieved witha summation, as follows:

$\begin{matrix}{{g(n)} = {\sum\limits_{{k = 1},2,{\ldots\mspace{11mu} L}}{{c\left( {k + {nL}} \right)}{r\left( {k + {nL}} \right)}}}} & {{Eq}.\mspace{14mu} 14} \\{\mspace{45mu}{= {\sum\limits_{{k = 1},2,{\ldots\mspace{11mu} L}}{b\left( \left\lfloor {\left( {k + {nL}} \right)/L} \right\rfloor \right)}}}} & {{Eq}.\mspace{14mu} 15} \\{\mspace{45mu}{{= {{Lb}(n)}},}} & {{Eq}.\mspace{14mu} 16}\end{matrix}$

where n is over all integers and k is over {1, 2, 3, . . . L}.

The gain factor L is just a scaling. We can recover b(n) by looking atthe sign of g(n) as follows:b′(n)=sign [g(n)]=sign [Lb(n)]  Eq. 17

In the absence of noise, b′(n)=b(n) decodes error free.

Let us consider the case when there is some error on g(n) due to noise.g(n)=Lb(n)+ε_(N)(n),  Eq. 18

where ε_(N)(n) represents an error due to noise interference.

We may try to recover b(n) by looking at the sign of g(n)b′(n)=sign(g(n))=sign(Lb(n)+ε_(N)(n)  Eq. 19

We will have a decoding error for large ε_(N)(n). Specifically, we havean error in b′(n) when:ε_(N)(n)·sign(Lb(n))>1  Eq. 20

That is, probability of error is dominated by the magnitude of ε_(N)(n):Prob(b′(n) Decision Error)=Prob(ε(n)sign(Lb(n))>1)  Eq. 21

This probability of error is controlled by the spreading gain which is afunction of L. Here we derive our selected L. Our spreading chip rateR_(c) will be R_(c)=2000 Chips/Second. Our theoretical transmission bitrate R_(b) (i.e., the rate of b(n)) was set to R_(b)≦25.6021 bps. Withthe redundancy of error corrective coding, our transmission symbol rateR_(sym) (i.e., the rate of data(m)) may have to be at least twice this,i.e., R_(sym)≧50. To obtain this symbol rate, we may choose from knowngood spreading patterns. An appropriate amount of spreading was thusfound with L=31 Chips/Symbol.

This L gives us our spreading gain. It can be shown that for everyhalving of bit rate, we get approximately 3 dB of spreading gain. Thatis,spreading gain=3*log₂(L)=14.8626  Eq. 22

Given that our PSK system had a required SNR of 8.3 dB, as described inmore detail below, we now find SNR≧−6.5626 dB.

In accordance with various embodiments of the present disclosure, theSSDH systems, methods, and devices may be built upon PSK modulation.Referring again to FIG. 2A, the PSK modulator 240 may be embodied asshown in FIG. 6, which depicts an exemplary block diagram of a PSKmodulator 600 in accordance with various embodiments of the presentdisclosure. In PSK modulation, all information is encoded into the phaseof a carrier tone. The phase will switch over time to send theinformation. Let σ(k) represent the phase envelope sequence 610 to bemodulated and sent, which may be defined as follows:σ(k) are elements of 1{, e ^(i2π(1/η)) , e ^(i2π(2/η)) , . . . e^(i2π((η−1)/η))}, for each discrete time index k,  Eq. 23

wherein j represents the unit imaginary number (j²=−1), and η representsthe number of phases used by the PSK modulator.

The relationship between continuous time, t, and discrete time, k, isgiven by the period T_(c).t=kT _(c)  Eq. 24k=└t/T _(c)┘,  Eq. 25

where └•┘ is the floor operator.

Smoothed phase transitions may be created by low pass filtering σ(k)with p(t).s(t)=Σ_(k)σ(k)p(t−kT _(c)),  Eq. 26

wherein s(t) represents the baseband phase modulated signal in thetransmitter, and filter 630, denoted as p(t), represents the square rootraise cosine pulse shaping filter with 60% roll off.

We may select p(t) to satisfy the Nyquist criteria. That is, when weconvolve s(t) with p(t) we obtain the following:s(kT _(c))*p(kT _(c))=σ(k)  Eq. 27

Let us modulate by multiplying s(t) by a carrier tone:u(t)=2 Real[s(t)e ^(j2πf) ^(c) ^(t)]  Eq. 28=s(t)e ^(j2πf) ^(c) ^(t) +s*(t)e ^(j2πf) ^(c) ^(t),  Eq. 29

wherein u(t) represents the pass band output 620 of the PSK modulator600, f_(c) represents a carrier frequency, and s*(t) represents thecomplex conjugate of s(t). Now u(t) may be produced by the PSK modulator600.

At the receiver side, the modulated signal 710, denoted as u(t), isdemodulated to compute the received phase envelope 720, denoted as ρ(k).FIG. 7 depicts an exemplary block diagram of a PSK demodulator 700 inaccordance with various embodiments of the present disclosure. In thepresent example, it is assumed that u(t) is obtained in the receiverwith no noise, voice interference, or synchronization issues. Thebaseband phase demodulated signal at the receiver, denoted as r(t), maybe given as follows:r(t)=u(t)e ^(−j2πf) ^(c) ^(t)  Eq. 30=s(t)+s*(t)e ^(−j4πf) ^(c) ^(t)  Eq. 31

At this point we convolve with the matched filter 730, denoted as p(t).We can assume the low pass filter effectively suppresses the secondterm, yielding:r(t)*p(t)=s(t)*p(t)  Eq. 32

Finally we sample at T_(c)ρ(k)=r(kT _(c))*p(kT _(c))  Eq. 33=s(kT _(c))*p(kT _(c))  Eq. 34=σ(k)  Eq. 35

Note that in this ideal noiseless example, we have recovered thetransmitted information ρ(k)=σ(k).

With noise, the performance of the PSK modulator/demodulator is afunction of T_(c) or R_(c)=1/T_(c). After collecting data withR_(c)=2000, it was determined that u(t) should transmit with a high SNRto achieve a bit error rate of 10⁻⁴. It was determined that PSK aloneshould have SNR≧8.3 dB.

In accordance with various embodiments of the present disclosure,transparency may be improved by reducing audible artifacts of spreadspectrum data. It has been observed that u(t) has an artifact referredto as a humming sound at approximately 1800 Hz. To improve upon this, an1800 Hz notch filter may be added. Thus, the AC notch filter 250depicted in FIG. 2A may comprise an 1800 Hz notch filter, in oneembodiment. In accordance with other embodiments, the AC notch filter250 may be implemented with respect to other carrier frequencies.

The cause of the humming sound is a slight DC offset in s(t). One canalternatively implement a DC notch filter on s(t). Thus, the DC notchfilter 260 depicted in FIG. 2B may be used to reject a zero frequency DCcomponent such thatσ(k)=DCNotch[c(k)b(└k/L┘)]  Eq. 36

wherein Eq. 36 replaces Eq. 11 for the output of the spreading encoder.

The offset is just strong enough to be perceptible by a sensitive ear.However, it is small enough that the effect of its removal is consideredto have negligible impact on the data transmitter/receiver.

In accordance with other embodiments of the present disclosure, thehumming sound may be reduced using other techniques. For example,instead of a notch filter, redundant bits may be inserted into the bitstream for spectral control of the DC bias. The redundant bits can beignored at the receiving end based on an agreed upon rule.

In addition, an artifact referred to as a slight buzzing sound has beenobserved in u(t). It was discovered that the cause of this buzzing soundwas the periodic nature of c(k). Note c(k) has a period of L given byc(k)=q((k−1)mod L)+1). Lengthening the period of c(k) may suppress thebuzzing sound. An effective solution was found that uses multiple Goldchip sequence generators which differ by their initialization points.Each provides a unique q_(i)(k). In generating c(k), every L chips weswitch to a new q_(i)(k). It was found that, with a suitable pseudorandom switching pattern, four Gold chip sequence generators provide thedesired suppression of the buzzing sound; however, a lesser or greaternumber of chip sequence generators may be used. For example, somebenefit may be found by using two Gold chip sequence generators.

FIG. 8 depicts a block diagram of an exemplary low buzz CDMA chipsequence generator 800 in accordance with various embodiments of thepresent disclosure. In accordance with such embodiments, the user select210 and the chip sequence generator 220 of FIG. 2A or 2B may be embodiedas the low buzz CDMA chip sequence generator 800 of FIG. 8.

Another audible artifact referred to as a beat was observed in thespread spectrum signal u(t). It was determined that the cause of thebeat was the limiting of σ(k) to only two phases. It was found thatincreasing the number of phases (e.g., at least four phases) helped tosuppress the beat. In some embodiments, the four phases may beapproximately 90° apart, although they need not be spaced evenly apart.It was further found that a σ(k) with at least eight (η=8) phases ismore effective for suppressing the beat. In some embodiments, the eightphases may be approximately 45° apart and randomly selected. This may beaccomplished by taking the output of the two phased spread spectrumencoder and rotating the phase by a psuedo random increment ofapproximately 45° every chip.

FIG. 9 depicts a block diagram of an exemplary phase randomizer 900 inaccordance with various embodiments of the present disclosure. Theoutput of a spread spectrum encoder may be fed into the phase randomizer900 and multiplied with a pseudo random phase pattern, as follows:σ(k)=λ(k)·spread spectrum encoder output,  Eq. 37

wherein λ(k) represents a pseudo random pattern such that λ(k) areselected from the phasor set {1, e^(jπ(1/4)), e^(jπ(1/2)), . . . ,e^(jπ(7/4))} for each discrete time index k.

The complex phasor λ may be generated by a pseudo random index. Thisindex may be produced by a 15-bit linear shift feedback register.

At the receiver side, the phase scrambling can be decoded by multiplyingthe demodulated signal by the complex conjugate of λ(k). FIG. 10 depictsa block diagram of an exemplary phase de-randomizer 1000.

FIG. 11A depicts a block diagram of an exemplary Audibly White Modulator1100 in accordance with one embodiment of the present disclosure. TheAudibly White Modulator 1100 produces a combined signal wherein thehidden data may more resemble the sound of natural white noise. Inaccordance with some embodiments, the hidden data may not be absolutelyquiet, but may be relatively quiet, relative to the voice signal. TheAudibly White Modulator 1100 is not intended to produce a sound thatmeets the mathematical definition of white noise, but rather, the noise(if any) heard by a human listener is intended to be perceived as whitenoise.

The Audibly White Modulator 1100 may comprise a low buzz CDMA chipsequence generator 1110 such as that depicted in FIG. 8. The AudiblyWhite Modulator 1100 may further comprise a spreading encoder 1120 suchas that depicted in FIG. 4. In another embodiment, the low buzz CDMAchip sequence generator 1110 may be considered as a component of thespreading encoder 1120. The Audibly White Modulator 1100 may furthercomprise a phase randomizer 1130 such as that depicted in FIG. 9. TheAudibly White Modulator 1100 may further comprise a PSK modulator 1140such as that depicted in FIG. 6. The Audibly White Modulator 1100 mayfurther comprise an AC notch filter 1150 for attenuating a desiredcarrier frequency, such as 1800 Hz or other carrier frequency.

In accordance with another exemplary embodiment as depicted in FIG. 11B,an Audibly White Modulator 1160 may comprise a DC notch filter 1170,instead of the AC notch filter 1150.

A block diagram of an exemplary embodiment of an Audibly WhiteDemodulator 1200 is depicted in FIG. 12. The Audibly White Demodulator1200 may comprise a PSK demodulator 1210 such as the PSK demodulator 700depicted in FIG. 7 and described herein. The Audibly White Demodulator1200 may further comprise a phase de-randomizer 1220 such as the phasede-randomizer 1000 depicted in FIG. 10 and described herein. The AudiblyWhite Demodulator 1200 may further comprise a spreading decoder 1230such as the spreading decoder 500 depicted in FIG. 5 and describedherein. The Audibly White Demodulator 1200 may further comprise a lowbuzz CDMA chip sequence generator 1240 such as the low buzz CDMA chipsequence generator 800 depicted in FIG. 8 and described herein. In someembodiments, the low buzz CDMA chip sequence generator 1240 may beconsidered as a component of the spreading decoder 1230.

Reference is now made to FIG. 13 which depicts a block diagram of anexemplary data and voice mixer 1300 in accordance with variousembodiments of the present disclosure. A voice signal 1310 to betransmitted is denoted by voice(t). A delay unit 1320 may be included toalign the voice signal 1310 for proper cancellation.

The binary sequence 1330 to be transmitted is denoted by data(m). Thebinary sequence 1330 may be fed into an FEC (Forward Error Correction)encoder 1340. The output of the FEC encoder 1340 may be fed into a syncinserter 1350. Various embodiments of the FEC encoder 1340 and the syncinserter 1350 are described below in more detail. The output of the syncinserter 1350, denoted as b(n), may be fed into a voice interferencecanceller 1360. Exemplary embodiments of the voice interferencecanceller 1360 may be found in U.S. application Ser. No. 11/148,087, thecontents of which have been incorporated herein by reference.

The output of the voice interference canceller 1360 may be fed into anaudibly white modulator 1370 such as that depicted in FIG. 11A or 11B.The output of the audibly white modulator 1370, denoted as u(t), may befed into a masking shaper 1380. Various embodiments of the maskingshaper 1380 are described below in more detail. The output of themasking shaper 1380, denoted as μ(t), may be added with the output ofthe delay unit 1320 to produce a transmitter signal denoted as x(t). Thetransmitter signal 1390 may be used as an input to, for example, atelephone channel or other communication channel.

Reference is now made to FIG. 14 which depicts a block diagram of anexemplary embodiment of an FEC encoder 1400 in accordance with variousembodiments of the present disclosure. The FEC encoder 1400 may comprisea Reed-Solomon encoder 1410, a block interleaver 1420, a convolutionalencoder 1430, and a constellation mapper 1440. In connection withimplementing Forward Error Correction methods, a concatenated code withan inner soft decoded convolutional code and an outer algebraicallydecoded Reed-Solomon code may be used.

The inverse may be used on the receiver side, as shown in FIG. 15 whichdepicts a block diagram of an exemplary FEC decoder 1500 in accordancewith various embodiments of the present disclosure. The FEC decoder 1500may comprise a Viterbi decoder 1510, a block deinterleaver 1520, and aReed-Solomon decoder 1530.

Reference is now made to FIG. 16 which depicts a block diagram of anexemplary embodiment of a sync pattern inserter 1600 in accordance withvarious embodiments of the present disclosure. A short reference patternof a known sign may be transmitted. In one embodiment, a 10-symbolpattern may be chosen as follows:b _(sync)(n)={+1,−1,−1,−1,+1,1,−1,+1,−1,+1}.  Eq. 38

The more often this is transmitted, the more often we can synchronize orresynchronize. However the overall bit rate is lowered. In oneembodiment, the pattern may be sent after every four cycles of theinterleaver.

To make the detection more reliable on the receiver, an additionalmodification may be made within the transmitter's Low Buzz CDMA ChipSequence Generator. As described above, four Gold chip sequencegenerators may be provided to reduce the buzz throughout the frame.During the transmission of the sync, a fifth orthogonal user dependentGold chip sequence generator may be used.

Reference is now made to FIG. 17 which depicts a block diagram of anexemplary embodiment of a masking shaper 1700 in accordance with variousembodiments of the present disclosure. The masking shaper 1700 maycomprise a spectral shape extractor 1710, an exemplary embodiment ofwhich is shown in FIG. 18. The masking shaper 1700 may further comprisea masking shaping filter (MSF) 1720, an exemplary embodiment of which isshown in FIG. 19. The MSF may be used to apply a spectral shape to thesignal u(t).

The time domain signals may be generally band limited withinapproximately 0 Hz to approximately 4000 Hz in a typical telephonechannel. This frequency band may be divided into a number of subbands,for example, 32 subbands of approximately 125 Hz each. A smaller orlarger number of subbands may be used. The subbands may be indexed asfollows:i=subband index,  Eq. 39

wherein i is within the set {0, 1, 2, . . . , 31}.

The spectral content of u(t) may be computed over a windowed periodabout time t in each subband i with the Analysis operator (1910) asfollows:U(i,t)=Analysis[u(t)],  Eq. 40

wherein U(i,t) is a complex signal.

This analysis can be implemented along with a counterpart Synthesis(1920) with perfect reconstruction.u(t)=Synthesis[U(i,t)]=Synthesis[Analysis[u(t)]]  Eq. 41

A spectral shape may be applied to U(i,t) by means of a spectral gainΦ(i,t).μ(t)=Synthesis[Analysis[u(t)]·Φ(i,t)]  Eq. 42=MSF[u(t)]  Eq. 43

The inverse operator of the Masking Shaping Filter is the InverseShaping Filter (ISF).u(t)=Synthesis[Analysis[μ(t)]·(1/Φ(i,t))]  Eq. 44=ISF[μ(t)]  Eq. 45

As the inversion may not be perfect, we have the following:u(t)≈ISF[MSF[u(t)]]  Eq. 46

The approximation approaches equivalency when Φ(i,t) varies slowly overtime.

The final signal to be transmitted into the communication channel may begiven by x(t) as follows:x(t)=voice(t−ζ _(voice))+μ(t),  Eq. 47

where ζ_(voice) represents a transmit delay for the voice signal. Alistener may desire that the addition of the signal μ(t) sound like alow level white noise. Therefore, x(t) may sound much like the originalvoice(t) with additive noise. This noise can be kept low enough that itspresence can be relatively undetectable compared to noise in voice(t)and additive noise of the telephone channel or other communicationchannel.

In accordance with various embodiments, it may be desirable to achieve abit error rate on the receiver of approximately 10⁻⁴ or better. This maybe accomplished by maximizing the SNR of the received version of x(t).Note from this perspective, voice(t) is noise. The telephone channel orother communication channel adds noise as well. The only signal is μ(t).Thus, it may be desirable to maximize the power at which μ(t) istransmitted. Increasing this power, however, may be audiblydisadvantageous to listeners of voice(t) in x(t). The masking effectgives an upper limit of power at which μ(t) can be transmitted. It saysthat we can transmit μ(t) at as much as approximately 13 dB belowvoice(t) and it will be substantially undetectable to the human ear. Toemploy this masking, a spectral and time domain envelope may be providedfor μ(t) that is near to that of voice(t). We can apply this gain andenvelope with Φ(i,t). The spectral shape may be extracted as follows:

$\begin{matrix}{\mspace{79mu}{{{VOICE}\;\left( {i,t} \right)} = {{Analysis}\left\lbrack {{voice}\;(t)} \right\rbrack}}} & {{Eq}.\mspace{14mu} 48} \\{\mspace{79mu}{{{RMSVOICE}\left( {i,t} \right)} = \left( {{LPF}\left\lbrack {{{VOICE}\left( {i,t} \right)}}^{2} \right\rbrack} \right)^{1/2}}} & {{Eq}.\mspace{14mu} 49} \\{{\Phi\left( {i,t} \right)} = \left\{ \begin{matrix}{{{RMSVOICE}\left( {i,t} \right)} \cdot {\Psi(i)}} & {{{RMSVOICE}\left( {i,t} \right)} > {{NOISEFLOOR}(i)}} \\{\Psi(i)} & {{{RMSVOICE}\left( {i,t} \right)} \leq {{NOISEFLOOR}(i)}}\end{matrix} \right.} & {{Eq}.\mspace{14mu} 50}\end{matrix}$

An exemplary embodiment of a spectral shape extractor 1800 is shown inFIG. 18. The spectral extractor 1800 may comprise a square law envelopedetector. It works on subbands to generate the spectral shape. Forexample, 32 envelope detectors may be implemented, one for each subband.

At the end, each band may be multiplied by a gain Ψ(i) (which gain maybe less than 1). This gain may be tuned to obtain the correct levels onμ(t). In one embodiment, we wish to be 13 dB below voice(t). Also, Ψ(i)may be used to shape μ(t) to give a natural noise sound. Furthermore, itwas found that attenuating the high and low bands of Ψ(i) minimizesaudible rough artifacts in x(t).

In accordance with various embodiments of the present disclosure, alower limit may be placed on the spectral gain Φ(i,t). For μ(t) tosurvive the telephone or other channel, it should not drop below acertain energy level in any part of the spectrum. The lower limit iscontrolled by the noise floor of the voice signal, as discussed in moredetail below.

The Masking effect may be used in the transmitter by the Masking Shaper1700 of FIG. 17 and subsequently added with the voice signal itself.

Reference is now made to FIG. 20 which depicts a block diagram of anexemplary whitening equalizer 2000 at the receiving end in accordancewith various embodiments of the present disclosure. The whiteningequalizer 2000 may comprise a spectral shape extractor 2010. Thewhitening equalizer 2000 may further comprise an Inverse Shaping Filter(ISF) 2020.

A model of attenuation and noise for a Telephone Channel 2030 may begiven as follows:y(t)=h·x(t)+noise(t),  Eq. 51

wherein h represents the channel gain.

The inverse shaping filter may be performed on the received signal suchthat w(t) is given as follows:w(t)=ISF[y(t)]  Eq. 52=ISF[h·x(t)+noise(t)]  Eq. 53=ISF[h·μ(t)+h·voice(t)+noise(t)]  Eq. 54=u(t)+ISF[h·voice(t)+noise(t)]  Eq. 55=u(t)+δ(t),  Eq. 56where δ(t)=ISF[h·voice(t)+noise(t)]  Eq. 57

The inverse shaping filter 2020 gives back the modulated data u(t) plusinterference.

To run the inverse shaping filter, the Spectral Shape Extraction isperformed on y(t). For the inverse shaping to work properly, the outputof this extractor should be h·Φ(i,t). That is the linear scale of itscounterpart in the transmitter. This is complicated by the non-linearityof lower limiting in the extractor. A solution was found in which thelower limit is given as a function of the noise floor estimate of thesignal.

In addition, the inverse shaping filter 2020 acts as a channelequalizer. In this example, it inverses h. In general, it will inverse achannel shape given by H(f). In addition, the shaping filter acts as awhitening filter for δ(t). This could be seen by the fact that Φ(i,t) isthe shape of the voice(t), and therefore ISF[voice(t)] should berelatively white. This is beneficial as it may be desirable to decodethe data may with a whitened interference.

There exist various ways of estimating the noise floor. In accordancewith one embodiment of the present disclosure, the noise floor may beestimated as follows:

1) Compute the mean square on very small windows of signal.

2) Save the few smallest mean squares over a period of time.

3) Use the smallest mean squares to compute a root mean square.

4) As we converge, adjust size of window, the period, the method ofmean.

5) On the transmitter side put a lower bound on the root mean square toaccount for the noise on the channel and the noise for adding μ(t)itself.

6) The noise floor estimate is given by the root mean square.

Reference is now made to FIG. 21 which depicts a block diagram of anexemplary data and voice separator 2100 in accordance with variousembodiments of the present disclosure. The data and voice separator 2100may comprise a whitening equalizer 2110 such as the whitening equalizer2000 shown in FIG. 2000 and described above. The data and voiceseparator 2100 may comprise a tracking receiver 2120, which may comprisean FEC decoder such as the FEC decoder 1500 of FIG. 15. The output ofthe data and voice separator 2100 includes an estimate of the voice(t),which is denoted as voice′(t), and an estimate of data(m), which isdenoted as data′(m−ζ_(data)).

The above-described modules and devices may be embodied in hardware,software, firmware, or a combination thereof. Various embodiments of thepresent disclosure may find useful application in the fields of audioconferencing and video conferencing. Reference is now made to FIG. 22which depicts a block diagram of an exemplary conferencing system inaccordance with various embodiments of the present disclosure. Inaccordance with various embodiments of the present disclosure, theconferencing system may provide for multipoint conferencing, i.e.,conferencing among three or more endpoints. As well, the conferencingsystem may provide for point-to-point conferencing, i.e., conferencingbetween two endpoints.

The conferencing system comprises a plurality of conference endpointssuch as speakerphones or other audio conferencing units, videoconferencing units, and other terminal devices. In the present example,there are shown four endpoints 2210, 2220, 2230, and 2240. The endpointscan be communicably coupled with each other via a network ofcommunication channels 2250, 2260, 2270, and 2280. The communicationchannels 2250, 2260, 2270, and 2280 may comprise wired or wirelesschannels, or both. For example, in some embodiments, any of thecommunication channels may comprise a telephone channel such as a POTS(Plain Old Telephone Service) channel; a radio channel such as acellular channel; or any other channel containing an analog section ofunknown gain. In one embodiment, one or more of the communicationchannels 2250, 2260, 2270, and 2280 operate under a standard such asG.711.

The conferencing system may further comprise a conference bridge 2290used for multipoint conferencing. The conference bridge 2290 may becommunicably coupled to each of the endpoints 2210, 2220, 2230, and 2240via the communication channels 2250, 2260, 2270, and 2280, respectively.

Endpoints 2210, 2220, 2230, and 2240 may comprise, for example,speakerphones, each comprising one or more microphones and one or morespeakers. Endpoints 2210, 2220, 2230, and 2240 may generally compriseany audio conferencing unit, video conferencing unit, or other terminaldevice capable of sending and receiving analog voice signals. For easeof understanding, endpoints 2210 and 2220 are described below in thecontext of transmitting, while endpoints 2230 and 2240 are described inthe context of receiving. It should be understood, however, that eachendpoint 2210, 2220, 2230, and 2240 may be capable of both transmittingand receiving voice signals.

Endpoint 2210 may comprise a voice source 2212. Endpoint 2210 mayfurther comprise a data and voice mixer 2214 operable to embed data in avoice signal. The data and voice mixer 2214 may be embodied as amachine-readable medium having thereon a program executable by aprocessor in the endpoint 2210. In some embodiments, the data and voicemixer 2214 may be separate from the endpoint 2210. For example, the dataand voice mixer 2214 may be embodied in a separate modem device. Thedata and voice mixer 2214 may include features such as those describedin connection with FIGS. 1 and 13 above. A data source 2216 may providean input to the data and voice mixer 2214. In some embodiments, the datasource 2216 may comprise a separate device, such as, for example, acomputer (e.g., desktop, laptop, or handheld, etc.), a personal dataassistant (PDA), a projector, a video camera, a Bluetooth® whiteboard,or other device capable of providing data. In some embodiments, the datasource 2216 may be embodied in the endpoint 2210.

Similarly, endpoint 2220 may comprise a voice source 2222. Endpoint 2220may further comprise a data and voice mixer 2224 operable to embed datain a voice signal. The data and voice mixer 2224 may be embodied as amachine-readable medium having thereon a program executable by aprocessor in the endpoint 2220. In some embodiments, the data and voicemixer 2224 may be separate from the endpoint 2220. For example, the dataand voice mixer 2224 may be embodied in a separate modem device. Thedata and voice mixer 2224 may include features such as those shown inFIG. 1 or FIG. 13 and as described above. A data source 2226 may providean input to the data and voice mixer 2224. In some embodiments, the datasource 2226 may comprise a separate device, such as, for example, acomputer (e.g., desktop, laptop, or handheld, etc.), a personal dataassistant (PDA), a projector, a video camera, a Bluetooth® whiteboard,or other device capable of providing data. In some embodiments, the datasource 2226 may be embodied in the endpoint 2220.

Endpoint 2230 may comprise a voice sink 2232. Endpoint 2230 may furthercomprise a data and voice separator 2234. The data and voice separator2234 may be embodied as a machine-readable medium having thereon aprogram executable by a processor in the endpoint 2230. In someembodiments, the data and voice separator 2234 may be separate from theendpoint 2220. For example, the data and voice separator 2234 may beembodied in a separate modem device. The data and voice separator 2234may include features such as those shown in FIG. 21 and described above.The data and voice separator 2234 may provide one or more data inputs todata sink 2236. In some embodiments, more than one data input to datasink 2236 may comprise more than one physical data connection (e.g.,cables, memory locations, or multiple data buses, etc.) to distinguisheach of the data inputs from each other. In some embodiments, more thanone data input to data sink 2236 may comprise only one physical dataconnection using logical means to distinguish each of the inputs fromeach other (e.g., Internet Protocol, addressable data bus, ormultiplexing, etc.). An example for the purpose of providing more thanone data input to data sink 2236 is so that the data and voice separator2234 may distinguish the data originating from endpoint 2210 and thedata originating from endpoint 2220 as two separable inputs to the datasink 2236. In some embodiments, the data sink 2236 may comprise aseparate device, such as, for example, a computer (e.g., desktop,laptop, or handheld, etc.), a personal digital assistant (PDA), adisplay device, or other device capable of receiving data. In someembodiments, the data sink 2236 may comprise multiple devices, such as adevice for each data signal. In some embodiments, the data sink 2236 maybe embodied in the endpoint 2230. In such embodiments, for example, thedata may comprise control data for controlling the endpoint 2230.

Endpoint 2240 may comprise a voice sink 2242. In the present example,endpoint 2240 may not include a data and voice separator or a data sink.Accordingly, the received signal of mixed data and voice can still bebranched into a signal and reproduced as sound by the endpoint 2240. Tothe voice sink 2242, the received signal is treated as a voice signal,and the data is ignored. For conference participants using endpoint2240, the embedded data may be ignored because the sound of the data maybe substantially humanly imperceptible or may sound like white noise, inaccordance with various embodiments of the present disclosure.

The embedded data may comprise any of a variety of types of data, suchas, for example, text, contact information, presentation information, orcontrol commands for a remote device, etc. The data can be used by theaudio or video conference equipment to automate many routine tasks, suchas, for example, exchanging parties' phone numbers and names, etc.; orremotely control related equipment, e.g., adding a video portion of theconference call to make it a video conference call or transmitting a webaddress of a web site of interest.

The data embedded in the audio may also be used as a means forintellectual property rights management, including copyright protection.For example, a digital watermark may be embedded into audio to formwatermarked content, such as watermarked music or speech, for example.The watermark may be used to evidence proof of ownership, controlunauthorized access to the content, and trace unauthorized copies of thecontent.

The foregoing examples are provided as illustrative examples and are notintended to be exhaustive. Other types of data than can be embedded inthe audio are within the scope of the invention.

In the current disclosure, speech signal or voice signal generallyrefers to an audio signal in an audio system, which system is operableto process such audio signal. The speech signal or voice signal is notnecessarily human speech. It can be any audio signal or sound. The bitstream or digital data include any digital data embedded in or added tothe audio signal.

Furthermore, various features of the present disclosure may be ofbenefit when used with other types of cover media, such as images andvideo, etc. For example, data may be embedded in images or videosignals, and humanly visible artifacts may be suppressed in order toprovide enhanced concealment of the data and improved transparency.

While illustrative embodiments of the invention have been illustratedand described, it will be appreciated that various modifications can bemade therein without departing from the spirit and scope of theinvention. To the extent that such modifications fall within the scopeof the appended claims and their equivalents, they are intended to becovered by this patent.

1. A method of preparing an analog audio signal and a digital bit streamfor transmission via an analog communication channel, the methodcomprising: generating a chip sequence; combining the digital bit streamand the chip sequence, to form a spread spectrum sequence; modulatingthe spread spectrum sequence onto the audio signal, to form a modulatedsignal; and suppressing one or more noise-like artifacts of themodulated signal, wherein the act of suppressing comprises rotating aphase of the spread spectrum sequence by a pseudo-randomly selectednumber of increments every chip.
 2. The method of claim 1, wherein theact of suppressing comprises applying a notch filter in a narrow band inorder to attenuate the modulated signal near a carrier frequency.
 3. Themethod of claim 1, wherein the pseudo-randomly selected number ofincrements comprise a phase rotation of approximately 90 degrees orless.
 4. The method of claim 1, wherein the act of generating comprisesperiodically pseudo-randomly selecting the chip sequence from one of aplurality of chip sequence generators.
 5. The method of claim 4, whereinthe plurality of chip sequence generators comprise at least four Goldchip sequence generators.
 6. The method of claim 1, wherein the act ofmodulating comprises modulating a phase of the audio carrier signal. 7.The method of claim 1, wherein the analog communication channelcomprises a telephone channel.
 8. The method of claim 1, wherein theanalog communication channel comprises a radio channel.
 9. The method ofclaim 1, wherein the digital bit stream comprises information pertainingto an intellectual property right in the analog audio signal.
 10. Themethod of claim 1, further comprising: demodulating a received signal,to produce a demodulated signal; de-randomizing the demodulated signal,by multiplying the demodulated signal by a complex conjugate of a pseudorandom phase pattern, to produce a phase envelope sequence; andmultiplying the phase envelope sequence by the chip sequence, to producethe recovered bit stream.
 11. A non-transitory machine-readable mediumhaving embodied thereon a program, the program being executable by amachine to perform the method of claim
 1. 12. An audio conferencingendpoint, comprising: at least one microphone; an audio and data mixercommunicably coupled to the at least one microphone, the audio and datamixer comprising: a first chip sequence generator operable to generate afirst chip sequence; a spreading encoder operable to combine a digitalbit stream and the first chip sequence, to form a spread spectrumsequence; a phase randomizer operable to rotate a phase of the spreadspectrum sequence by a pseudo-randomly selected number of incrementsevery chip; and a modulator operable to modulate the rotated spreadspectrum sequence onto an analog audio signal received from the at leastone microphone, to form a modulated signal; at least one speaker; and anaudio and data separator communicably coupled to the at least onespeaker, the audio and data separator comprising: a demodulator operableto demodulate a received signal, to produce a demodulated signal; aphase de-randomizer operable to de-randomize the demodulated signal, bymultiplying the demodulated signal by a complex conjugate of a pseudorandom phase pattern, to produce a phase envelope sequence; a secondchip sequence generator, operable to generate a second chip sequence;and a spreading decoder operable to multiply the phase envelope sequenceby the second chip sequence, to reconstruct a received bit stream. 13.The endpoint of claim 12, wherein the first chip sequence isperiodically pseudo-randomly selected from one of a plurality of chipsequence generators.
 14. The endpoint of claim 13, wherein the pluralityof chip sequence generators comprise at least four Gold chip sequencegenerators.
 15. The endpoint of claim 12, wherein the second chipsequence is periodically pseudo-randomly selected from one of aplurality of chip sequence generators.
 16. The endpoint of claim 15,wherein the plurality of chip sequence generators comprise at least fourGold chip sequence generators.
 17. The endpoint of claim 12, wherein thepseudo-random increment comprises approximately 45 degrees.
 18. Theendpoint of claim 12, wherein the audio and data mixer furthercomprises: a notch filter coupled to the modulator, wherein the notchfilter is operable to attenuate the modulated signal near a carrierfrequency.
 19. The endpoint of claim 12, wherein the modulator comprisesa PSK modulator, and wherein the demodulator comprises a PSKdemodulator.
 20. The endpoint of claim 12, wherein the digital bitstream comprises information pertaining to an intellectual propertyright in the analog audio carrier signal.
 21. The endpoint of claim 12,wherein the digital bit stream comprises control data for controllingoperation of a geographically remote conferencing endpoint.
 22. An audioconferencing system, comprising: a plurality of geographically remoteendpoints; and a conference bridge communicably coupled to each of theplurality of endpoints via at least one communication channel; whereinat least one of the plurality of endpoints comprises: at least onemicrophone; and an audio and data mixer communicably coupled to the atleast one microphone, the audio and data mixer comprising: a first chipsequence generator operable to generate a first chip sequence; aspreading encoder operable to combine a digital bit stream and the firstchip sequence, to form a spread spectrum sequence; a phase randomizeroperable to rotate a phase of the spread spectrum sequence by apseudo-randomly selected number of increments every chip; and amodulator operable to modulate the rotated spread spectrum sequence ontoan analog audio signal received from the at least one microphone, toform a modulated signal; and wherein at least another one of theplurality of endpoints comprises: at least one speaker; and an audio anddata separator communicably coupled to the at least one speaker, theaudio and data separator comprising: a demodulator operable todemodulate a received signal, to produce a demodulated signal; a phasede-randomizer operable to de-randomize the demodulated signal, bymultiplying the demodulated signal by a complex conjugate of a pseudorandom phase pattern, to produce a phase envelope sequence; a secondchip sequence generator, operable to generate a second chip sequence;and a spreading decoder operable to multiply the phase envelope sequenceby the second chip sequence, to reconstruct a received bit stream. 23.The system of claim 22, wherein the at least one communication channelcomprises a Plain Old Telephone System channel.
 24. The system of claim22, wherein the at least one communication channel comprises a radiochannel.
 25. The system of claim 22, wherein at least another one of theplurality of endpoints is operable to receive a modulated signal andreproduce the received signal as sound, and is not operable to separatemodulated data from the received modulated signal.
 26. The system ofclaim 22, wherein the digital bit stream comprises informationpertaining to an intellectual property right in the analog audio signal.27. The system of claim 22, wherein the digital bit stream comprisescontrol data for controlling operation of one or more of the endpoints.